塔里木大火成岩省二叠纪碱性煌斑岩的岩石成因和深部地球动力学过程  

Petrogenesis and Deep Dynamic Processes of Early Permian Alkaline Lamprophyres in Tarim Large Igneous Province,NW China

作　　者：曹俊 陈苗苗[1,3] 万淑敏 王慧丽 易辉 雷恒聪 Cao Jun;Chen Miaomiao;Wan Shumin;Wang Huili;Yi Hui;Lei Hengcong(State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,China;MOE Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,Central South University,Changsha 410083,China;School of Earth Sciences,East China University of Technology,Nanchang 330013,China)

机构地区：[1]东华理工大学核资源与环境省部共建国家重点实验室,江西南昌330013 [2]中南大学有色金属成矿预测与地质环境监测教育部重点实验室,湖南长沙410083 [3]东华理工大学地球科学学院,江西南昌330013

出　　处：《地球科学》2024年第7期2448-2474,共27页Earth Science

基　　金：国家自然科学基金项目(No.42063005);有色金属成矿预测与地质环境监测教育部重点实验室(中南大学)开放基金项目(No.2021YSJS19);南京聚谱检测科技有限公司2021年度开放基金项目(No.2021-10010);江西省自然科学基金项目(No.20202BABL213031)。

摘　　要：二叠纪塔里木大火成岩省以岩浆活动持续时间长、岩石类型复杂、巨量富铁碱性玄武岩为特征而区别于世界上其他以拉斑玄武岩为主体的大火成岩省,关于其地幔源区组分特征和成因仍然存在争议.选择塔里木大火成岩省西北缘瓦吉里塔格碱性煌斑岩岩脉为研究对象,通过锆石LA-ICP-MS U-Pb定年厘定这些碱性煌斑岩岩浆活动时间,并利用全岩主微量元素和Sr-Nd-Pb-Mg同位素以及单矿物成分分析,揭示其成因和塔里木大火成岩省形成的深部地球动力学过程.锆石LA-ICP-MS U-Pb定年结果限定了瓦吉里塔格碱性煌斑岩侵位年龄为279±1 Ma,属于塔里木大火成岩省第二期岩浆活动的产物.这些煌斑岩呈典型斑状全自形结构,斑晶矿物有橄榄石、单斜辉石、角闪石和黑云母,基质主要由斜长石、单斜辉石、角闪石、黑云母和钛磁铁矿等微晶组成.瓦吉里塔格碱性煌斑岩具有低SiO_(2)(43.5%~49.4%),高Fe_(2)O_(3)t(9.32%~15.50%)、TiO_(2)(2.28%~4.58%),Mg^(#)值在43.6~52.9,富集地幔相容元素(Ni、Cr)的特征,同时高Na_(2)O(2.58%~5.50%)和低K_(2)O/Na_(2)O比值(0.31~0.78)则反映了钠质岩石的属性.在微量元素上富集轻稀土元素、大离子亲石元素和高场强元素,具有弱的Nb-Ta正异常以及K、Sr、Ti、Zr-Hf负异常.它们的(^(87)Sr/^(86)Sr)_(i)变化于0.70436~0.70534之间,ε_(Nd)(t)值变化于-1.88~+1.10之间,(^(206)Pb/^(204)Pb)_(i)值为17.19~17.89.其元素和Sr-Nd-Pb同位素地球化学特征与常见的OIB型碱性玄武岩相似,但却具有比正常玄武岩更轻的Mg同位素组成(δ^(26)Mg=-0.78‰~-0.57‰).瓦吉里塔格碱性煌斑岩的原始岩浆应是含碳酸盐化榴辉岩的地幔柱低程度部分熔融的产物,并且部分发生了地幔柱-岩石圈地幔相互作用.地幔柱-俯冲蚀变洋壳相互作用是控制塔里木大火成岩省复杂岩石组合的关键因素.The Tarim Large Igneous Province is characterized by long duration of magmatism,complex rock types and wide distribution of iron-rich alkaline basalts,although the source and petrogenesis of magmatism associated with it remain disputed.Here we chose the Wajilitag alkaline lamprophyres in the northwestern margin of the Tarim Large Igneous Province to precisely determine their emplacement ages,constrain its petrogenesis and discuss the deep dynamic processes involved in the formation of the Tarim Large Igneous Province using LA-ICP-MS zircon U-Pb dating,mineral and whole-rock geochemistry.Zircon U-Pb geochronology indicates that the Wajilitag alkaline lamprophyres formed at 279±1 Ma,belonging to the second phase of Tarim Large Igneous Province magmatism.The lamprophyre is characterized by a panidiomorphic-porphyritic texture imparted by olivine,clinopyroxene,amphibole and biotite set in a groundmass of plagioclase,clinopyroxene,amphibole,biotite and titanomagnetite microcrysts.These rocks have low SiO_(2)(43.5%-49.4%),high Fe_(2)O_(3)t(9.32%-15.50%),high TiO_(2)(2.28%-4.58%),and Mg^(#)numbers of 43.6-52.9,and are enriched in mantle compatible elements(Ni,Cr).Meanwhile,they also show high Na_(2)O(2.58%-5.50%)and low K_(2)O/Na_(2)O ratios(0.31-0.78),highlighting their sodic characters.Fractionated chondrite normalized REE patterns indicates involvement of an enriched mantle source from within the garnet stability field whereas slightly negative K,Sr,Ti and Zr-Hf anomalies displayed on the primitive mantle normalized multielement spidergram highlight involvement of a subducted component in the mantle source.Bulk-rock(^(87)Sr/^(86)Sr)_(i)(0.70436-0.70534),ε_(Nd)(t)(-1.88-+1.10)and(^(206)Pb/^(204)Pb)_(i)(17.19-17.89)of the Wajilitag alkaline lamprophyres indicate derivation from a slightly depleted mantle source similar to that of asthenospheric magmas such as OIB.Notably,theδ^(26)Mg values of the Wajilitag alkaline lamprophyres are typically lighter than those of the normal mantle source.The primitive magmas of the

关 键 词：碱性煌斑岩 MG同位素 塔里木大火成岩省 地幔柱 俯冲蚀变洋壳 岩石学 

分 类 号：P581[天文地球—岩石学]